This invention relates to developer material, and more particularly to powdered developer material capable of color-reacting with dye or dye precursor.
A developer sheet has been conventionally formed as a specific sheet by dispersing developer material in an aqueous solvent in an ultrafine particle form, adding binder and additives to the dispersed solution and then coating it on paper. An image forming techinique using the developer sheet thus formed is disclosed in Japanese Unexamined Published Patent Applications No. 58-88739, No. 59-30537 and No. 59-137944.
The image forming technique as described above belongs to any type of technique in which two or more components separated from one another are contacted with one another due to a physical force such as pressure, temperature, etc. to react with one another, and then optical characterisitics such as light-absorbing region, light-absorbing intensity, etc. of the components are changed to record an information in accordance with the physical force. For example, there is an image forming technique utilizing a microcapsule sheet comprising a sheet coated with microcapsules having mechanical strength variable in accordance with light incident thereto and encapsulating colorless or slightly colored dye or dye precursor, and a developer sheet coated with developer material color-reactable with the dye or dye precursor encapsulated in the microcapsules. In this technique, when any kind of photosensitive recording medium coated with the microcapsules which has been exposed to light is superposed over the developer sheet under pressure to perform a pressure-developing process, some microcapsules are selectively ruptured due to a selective change in the mechanical strength to issue the colorless or slightly-colored dye or dye precursor from the ruptured microcapsules, and then the issued dye or dye precursor is color-reacted with developer material serving as a dye receptor coated on the developer sheet to form a visible image on the developer sheet.
In this type of technique, a visible image is formed only on a specifically manufactured sheet such as a developer sheet coated with a dye receptor (developer material). However, it has been frequently required in the art to form a visible image not only on the developer sheet, but also on any kind of medium such as a plain paper, post card or the like. In order to satisfy the above requirement, there has been proposed a developer material toner capable of color-reacting with microcapsules coated on a photosensitive and pressure-sensitive recording meidum, which is powdered and then electrostatically coated on any kind of medium. However, it has been difficult to obain an excellent developer material toner which is easily manufactured, has fluidity and sufficient pressure-fixability to any kind of medium such as plain paper, has stable fixing and developing properties for repetitive use, never adheres to a toner carrier and a toner case and has a high stability during storage period (that is, can be stored with no aggregation and no caking).
In view of the above condition, it has been proposed to add the above developer material toner with a softening agent in order to improve the pressure-fixablity to any kind of medium. However, this type of developer material toner has various problems, for example, it is difficult to finely pulverize the developer material, and even if it is pulverized, powdered developer material toners easily adhere to the toner carrier and the toner case to cause aggregation and caking therebetween. On the other hand, it has been proposed to provide the above developer material toner with a rigid resin in order to easily carry out a powdering process and improve chargeability, fluidity and storing capability. However, the developer toner thus obtained has remarkably-degraded pressure-fixability because the regid resin is generally more regid than the medium such as plain paper and thus it is not entagled in fibers consituting the medium even under pressure (that is, it is not fixed on the medium, but merely pressed against the surface of the medium). Accordingly, there has not been hitherto obtained powdered developer material which has excellent pressure-fixability to any kind of medium and sufficient chargeability, fluidity and storing capability.